A typical example of a stator for use in a rotating electrical machine such as a motor and a generator is disclosed in Japanese Unexamined Patent Publication No. 2001-25187, wherein the stator comprises a stator core having a circular ring shape, coils wound about magnetic teeth, and insulating members. Herein, the stator core corresponds to a lamination or stacking of magnetic steel sheets, from which a prescribed number of magnetic teeth project inwardly in the radial direction of the stator. The coils are wound about the magnetic teeth that are arranged in the circumferential direction of the stator, and the insulating members, each having a cylinder-like shape, are arranged to cover the magnetic teeth and are also arranged being sandwiched between the magnetic teeth and coils.
FIG. 5 shows a partial structure of a stator 30 in which the prescribed number of stator units 32 are arranged and assembled together in a circumferential direction with respect to magnetic teeth 31 respectively. FIG. 6 shows an exploded perspective view showing an assembly of each stator unit 32, which comprises a core unit 34 accompanied with an insulating member 37 consisting of a pair of insulating elements 35 and 36. Herein, the core unit 34 laminates plural magnetic steel sheets 33 to form a single magnetic tooth 34. The insulating elements 35 and 36 each having a square U-shape in section are assembled together with the core unit 34 from both sides, so that the core unit 34 is assembled together with the insulating member 37 having a cylinder-like shape, which covers the magnetic tooth 31. Then, a coil 38 is wound about the insulating member 37 as shown in FIG. 7.
In the above, a pair of the insulating elements 35 and 36 are connected together in such a way that they are mutually engaged with each other at the approximately center position in the stacking direction of the magnetic steel sheets forming the magnetic tooth 31, thus forming the insulating member 37 having a closed square cylinder shape. Prescribed dimensions are set to each of the insulating elements 35 and 36 to realize the least minimal thickness in consideration of strength and insulation. Therefore, prescribed dimensions are set to each of engagement portions 39a and 39b, which correspond to tip ends of the insulating elements 35 and 36, to realize the least minimal thickness. For this reason, under the engaged state of the insulating member 37, overlapping areas between the insulating elements 35 and 36 that are engaged with each other by the engagement portions 39a and 39b should be inevitably increased in thickness. Hence, the insulating members 37 substantially having the uniform thickness are arranged entirely with respect to outer surfaces of the magnetic teeth 31, which meet arrangements of the engagement portions 39a and 39b. 
Since the aforementioned stator units 32 arrange the insulating members 37 each having a square cylinder shape, the coils 38 wound about the exteriors of the insulating members 37 should be bent with small radiuses of curvature at every corner of the insulating members 37, while they may be wired substantially straight along with ‘flat’ surfaces of the insulating members 37 between corners.
Actually, however, due to the elasticity of the coil 38, the coil 38 may be partially separated from the flat surfaces of the insulating member 37 between corners. Therefore, the coil would not be tightly attached to the surfaces of the insulating member 37 between corners. That is, the coil 38 is greatly curved with a relatively large radius of curvature in such a way that it separates from the surface of the insulating member 37 at the approximately center position between adjacent corners.
The aforementioned phenomena that occurs in each stator unit 32 is shown in FIG. 7, wherein the coil 38 may be loosely wound about the insulating member 37 encompassing the magnetic tooth 31 in such a way that it would be greatly increased in dimensions in appearance in both the width and longitudinal direction of the core of the magnetic tooth 31 in proximity to the center position of the flat surface of the insulating member 37 between adjacent corners.
When the stator 30 is constituted by arranging the prescribed number of the aforementioned stator cores 32 in the circumferential direction thereof, the coils 38 must be greatly expanded outwardly in proximity to the center positions in the longitudinal direction of the core of the magnetic teeth 31, i.e., in the stacking directions of the magnetic steel sheets. This minimizes intervals of distance measured between adjoining stator units 32 at the center positions; in other words, minimal gaps are formed between adjoining stator units 32 at the center positions.
That is, even though sufficiently large intervals of distance are arranged between adjoining stator units 32, a bottleneck occurs due to the minimal gaps between adjoining stator units 32 at the center positions in the longitudinal direction of the core of the magnetic teeth 31. This causes difficulties in winding the coils 38 in further lengths about the insulating members 37 of the stator units 32. In addition, there is a problem in that intervals of distance between the magnetic teeth 31 cannot be reduced further.
It is an object of this invention to provide a stator that can increase numbers of turns of coils wound about stator units without changing dimensions regarding magnetic teeth, coil diameters, and the like, thus improving space factors of coils. In addition, it is another object of this invention to reduce intervals of distance between magnetic teeth without decreasing the numbers of turns of coils wound about stator units.